I'm starting with C++ and I'm trying to create a class program, however, when I try to run it appears the error: C++: Undefined reference to 'NameSpace::Class::Constructor. The code is shown below:
Header for ClassA:
//ClassA.h
#ifndef CLASSA_H
#define CLASSA_H
#include <string>
namespace ClassANameSpace
{
class ClassA
{
private:
std::string attribute1;
double attribute2;
public:
ClassA();
ClassA(std::string pAttribute1, double pAttribute2);
void setClassA(std::string pAttribute1, double pAttribute2);
std::string getAttribute1() { return attribute1; }
double getAttribute2() { return attribute2; }
};
}
#endif
Class A:
//ClassA.cpp
#include "ClassA.h"
using namespace ClassANameSpace;
ClassA::ClassA()
{
}
ClassA::ClassA(std::string pAttribute1, double pAttribute2)
{
setClassA(pAttribute1, pAttribute2);
}
void ClassA::setClassA(std::string pAttribute1, double pAttribute2)
{
attribute1 = pAttribute1;
attribute2 = pAttribute2;
}
Main:
// main.cpp
#include <iostream>
#include "ClassA.h"
using namespace std;
using namespace ClassANameSpace;
int main(int argc, char const *argv[])
{
ClassA classA ("string", 1.0);
return 0;
}
When I try to run it appears: undefined reference to `ClassANameSpace::ClassA::ClassA(std::__cxx11::basic_string<char, std::char_traits, std::allocator >, double)'
Someone can guide me to undestand what is going on?
Related
My code gives:
undefined reference to `NgramTree::generateTree(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int)'
collect2.exe: error: ld returned 1 exit status
error and I dont understand why.
Here is a sample of my code.
NgramTree.cpp
#include "NgramTree.h"
#include <fstream>
#include <string>
#include <iostream>
using namespace std;
void generateTree(string fileName, int n)
{
string line;
string ngram;
bool isWord = 1;
bool firstTime = 1;
ifstream myFile(fileName);
if (!myFile.is_open())
return;
...
NgramTree.h
#include <string>
class NgramTree {
public :
NgramTree (){ };
~NgramTree(){ };
void addNgram (std::string ngram );
int getTotalNgramCount ();
void printNgramFrequencies ();
bool isComplete ();
bool isFull ();
void generateTree(std::string fileName, int n);
};
main.cpp
#include <iostream>
#include <string>
#include <fstream>
#include "NgramTree.h"
using namespace std;
int main(){
NgramTree tree;
tree.generateTree("example.txt", 3);
return 0;
}
You need to add the class name in the cpp file. Write this, so that the compiler knows which class the method belongs to:
void NgramTree::generateTree(string fileName, int n) {
...
can someone please explain why the following code compilation fails with message "passing ‘const apple’ as ‘this’ argument of ‘int apple::foo()’ discards qualifiers", and how to resolve it.
#include <cstdlib>
#include <iostream>
#include <string>
#include <map>
using namespace std;
/*
*
*/
class apple{
private:
int a,b,c,d;
public:
int foo(){
return a+b+c+d;
}
};
class ball{
private:
map<apple,string> mp;
public:
void foo2(){
for(map<apple,string>::iterator it = mp.begin();it!=mp.end();++it){
cout<<it->first.foo()<<endl;
}
}
}
int main(int argc, char** argv) {
return 0;
}
Works for me: (added const at the end of foo() and ; on end of ball class). Class apple is a Key in std::map which is declared as const: typedef pair value_type; so accessing key should be also declared as const.
#include <map>
#include <iostream>
using namespace std;
class apple{
private:
int a,b,c,d;
public:
int foo() const {
return a+b+c+d;
}
};
class ball{
private:
map<apple,string> mp;
public:
void foo2(){
for(map<apple,string>::iterator it = mp.begin();it!=mp.end();++it){
cout<<it->first.foo()<<endl;
}
}
};
int main(int argc, char** argv) {
return 0;
}
How do I execute a member's function by passing the object and the member's function to another function in c++. I do understand the answer to my question is out there; however, I do not know what this is called. So far I created 2 files, exeFunc.h and exeFunc.cpp. Their code consist of:
exeFunc.h
/*
File: exeFunc.h
Header file for exeFunc Library.
*/
#ifndef EXEFUNC_H
#define EXEFUNC_H
#include "mbed.h"
#include "msExtensions.h"
#include "cfExtensions.h"
#include <map>
class exeFunc
{
public:
exeFunc(msExtensions &msExt, cfExtensions &cfExt);
private:
void _splitFuncFromCmd();
void _attachCallback();
msExtensions &_msExt;
cfExtensions &_cfExt;
//FunctionPointer _p;
};
#endif
exeFunc.cpp
/*
File: exeFunc.cpp
Execute functions in other Sensor libraries/classes
Constructor
*/
#include "mbed.h"
#include "ConfigFile.h"
#include "msExtensions.h"
#include "cfExtensions.h"
#include "exeFunc.h"
#include <map>
#include <string>
using namespace std;
exeFunc::exeFunc(msExtensions &msExt, cfExtensions &cfExt) : _msExt(msExt), _cfExt(cfExt)
{
//_cfExt.checkConfigForFirstStart();
//_p.attach(&_cfExt, &cfExtensions::checkConfigForFirstStart);
//_p.call();
}
void exeFunc::_splitFuncFromCmd()
{
}
void exeFunc::_attachCallback()
{
}
I wrote a completed example, may helps
class MyClass
{
public:
MyClass(int b)
:_b(b)
{
}
int Foo(int a)
{
return a * _b;
}
int _b;
};
typedef int (MyClass::*MFP)(int);
int get_result(MyClass* obj, MFP mfp)
{
int r = (obj->*mfp)(5); // 30
return r;
}
int _tmain(int argc, _TCHAR* argv[])
{
MFP mfp = &MyClass::Foo;
MyClass m(6);
get_result(&m, mfp);
return 0;
}
You call it by another function.if you have an independent function.
To be honesty your question is not completely clear.However :
int F(int,int,int);
int g();
//main scope
F(g(),a,b)
I have simple class in a header file: a.hh
#ifndef a_hh
#define a_hh
class a
{
public:
int i;
a()
{
i = 0;
}
};
#endif
Then i have a file:b.cc
#include <iostream>
#include "a.hh"
using namespace std;
int main(int argc, char** argv)
{
a obj;
obj.i = 10;
cout << obj.i << endl;
return 0;
}
>
Till this point everything is fine.
I compile the code and it compiles fine.
But as soon as i add a vector in the class:
#ifndef a_hh
#define a_hh
class a
{
public:
int i;
vector < int > x;
a()
{
i = 0;
}
};
#endif
I get a compilation error as below:
> CC b.cc
"a.hh", line 7: Error: A class template name was expected instead of vector.
1 Error(s) detected.
What is the problem with declaring a vector here as a member?
You need to #include <vector> and use the qualified name std::vector<int> x;:
#ifndef a_hh
#define a_hh
#include <vector>
class a{
public:
int i;
std::vector<int> x;
a() // or using initializer list: a() : i(0) {}
{
i=0;
}
};
#endif
Other points:
(as commented by EitanT) I removed the additional qualification a:: on the constructor
have a read of Why is "using namespace std" considered bad practice?
declaring a vector as a class member:
#include <iostream>
#include <vector>
using namespace std;
class class_object
{
public:
class_object() : vector_class_member() {};
void class_object::add_element(int a)
{
vector_class_member.push_back(a);
}
void class_object::get_element()
{
for(int x=0; x<vector_class_member.size(); x++)
{
cout<<vector_class_member[x]<<" \n";
};
cout<<" \n";
}
private:
vector<int> vector_class_member;
vector<int>::iterator Iter;
};
int main()
{
class_object class_object_instance;
class_object_instance.add_element(3);
class_object_instance.add_element(6);
class_object_instance.add_element(9);
class_object_instance.get_element();
return 0;
}
1.You need to #include <vector> and using namespace std, then a.hh just like below:
#ifndef a_hh
#define a_hh
#include <vector>
using namespace std;
class a
{
public:
int i;
vector <int> x;
a()
{
i = 0;
}
};
#endif
2. If you don't want to only use std namespace in all your code, you can specified the namespace before type, just like std::vector<int> x;
I am getting an error when I declare a class:
#include <iostream>
#include "testing/test.h"
#include <string>
using namespace std;
int main(void)
{
test links;
string content="this is an string";
links.getcont(content);
}
test.h
#ifndef TEST_H_
#define TEST_H_
#include<string>
using namespace std;
class test {
public:
string getcont(string content);
};
#endif /* TEST_H_ */
test.cpp
#include "test.h"
#include <iostream>
using namespace std;
string getcont(string content)
{
cout << content;
return content;
}
When I run this I get this error:
undefined reference to test::getcont(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)
Well , in your test.cpp file replace the getcont function for this
string test::getcont(string content){ //code here; }
The problem is that you are not saying that getcont is a member function of the test class.
Also, consider making it a const function and passing a const string reference
string
test::getcont( const string& content) const
{
return content;
}